This invention relates generally to domestic wood or coal heaters such as fireplace grates, stove grates, stoves and the like, and more particularly to grates and stoves wherein a forced convection of the exchanger fluid is employed to increase the heating efficiency.
Typically, the heating efficiency of a conventional fireplace or stove is extremely low for two reasons. First, the heat represented by the smoke and vapors is largely lost up the chimney. Second, the updraft in the chimney draws cold air from outside the house to filter into the room through the cracks in the doors and window casings, the cold air partially replacing the relatively warmer air occupying the room. In the past, many attempts have been made to increase the efficiency of fireplaces and stoves by extracting more of the waste heat and circulating it into the room. In some systems, this has taken the form of multiple convection channels in the brick surrounding the fireplace itself, both with and without auxiliary forced air equipment. Several manufacturers have developed gratings constituted of multiple U-shaped lengths of tubing disposed side by side, such that air could circulate through the tubes by natural convection. Many of these had complicated or difficult shapes and were costly to manufacture, being thus only moderately successful. Still other devices employed hollow tubing with forced convection, but these latter suffered from the drawback that only a limited area of the convectors was actually in contact with the glowing coals, which actually represent a large portion of the heat available from the fire. Accordingly, the efficiency of such systems, while better than that of an ordinary fireplace, still tended to be rather low.
Conventional open-fire stoves depended on natural convection to distribute their heat, and in consequence the area surrounding the stoves was overly hot whereas areas remote from the stove were too cold. Also, there was lacking the capability of circulating heated fluid from upper, lower and wall portions of the stove fire box, which portions received considerable heat by convection and radiation.